Mystery of the Disappearing Mouse

by Margaret J. Anderson

The field mouse died late in the afternoon. Its small, gray body lay half-hidden under a tuft of grass. by the next morning, it was gone. A patch of bare soil, about 12 inches from where the mouse had died, looked like a recently dug grave. But who had buried the small animal?

Soon after the mouse died, in a patch of woodland half a mile away, a black beetle with two bright orange bands across its wing covers raised its antennae to the breeze and detected the faint smell of the dead animal. The beetle immediately took to the air and flew straight toward the body, landing within a few feet of it. After locating the mouse, the beetle spent a few minutes exploring the area. Then it returned to the body and crawled under it.

Lying on its back, the beetle used its strong legs to lift the head end slightly and ease the mouse forward. The mouse moved slowly and steadily until it got hung up on some tough grass stems. The beetle came out to study the situation. It seemed to grasp the cause of the problem. A few minutes later it began to chew through the tangled grass to free the corpse.

Meantime, a second beetle had arrived at the scene. It, too, disappeared under the head of the mouse, where it was eventually joined by the first beetle. With the two beetles working together, the dead mouse began to move a little faster. Every now and then, one would emerge from behind the mouse and run round to the head end. They acted like a conveyor belt, moving the mouse along in a more-or-less straight line at a rate of about six inches an hour.

Under cover of darkness, the beetles moved their heavy burden to a patch of open ground, where they dug a grave and disposed of the body. They still worked from the underside of the corpse. If anyone had happened on the scene, they would have seen the mouse slowly sink into the ground, apparently burying itself!

Once the mouse was buried, bacteria and fungi began breaking down the animal's tissues, and the raw materials were slowly returned to the soil. This process is known as decomposition. But the beetles' goal was not to enrich the soil. Nor were they interested in making the countryside a more pleasant place by hiding dead and decaying bodies from sight. The beetles' aim was to provide nourishment for their children.

Unlike most insects, burying beetles are responsible parents. They feed and care for their young until they're grown and ready to face the world on their own. The two beetles that worked together on the mouse were a male and a female. Now that the corpse was buried and safe from other insects, such as wasps and flies that might also view the dead mouse as a tasty food supply, the beetles removed its fur and formed the body into a compact ball with a saucer-shaped depression on top. The female took time out to dig a short tunnel above the body, where she laid about 15 eggs.

When the eggs hatched, the adult beetles welcomed the grubs, or larvae, by rubbing their wing covers against their bodies to make a scratchy noise. The grubs crawled toward their parents, who popped food into their little open mouths, like birds feeding their nestlings. The youngsters thrived on the rich liquid diet of decomposing mouse. In just over a week they were ready for the next stage in their development. They turned into pupae. Since pupae do not eat, the parents had nothing more to do. They dug back up through the soil into the world of light and fresh air and flew off in search of more corpses.

Under the surface of what appears to be a barren patch of dirt, all sorts of creatures are at work. They are part of the unseen group of soil creatures that make life possible for the plants and animals that live above ground.

To learn more about burying beetles, read Children of Summer by Margaret J. Anderson
and Nature's Clean-Up Crew by Lorus J. Milne and Margery Milne.

Vocabulary

antennae: A pair of thin movable organs on the head of insects or animals.

conveyor belt: A device that uses a moving belt to move items from one place to another.